Daylight saving time is a system wherein timepieces are advanced by a predetermined period of time from the standard time during a specified period of from spring to fall. Daylight saving time is presently adopted by at least seventy countries. In the U.S., for example, the period of daylight saving time starts at 2 a.m. on the first Sunday of April and ends at 2 a.m. on the last Sunday of October, and during this period, timepieces are advanced by one hour. Stated more specifically with reference to FIG. 7, the period of daylight saving time in 2001 AD starts at 2 a.m. on the first Sunday of April, i.e., April 1. Accordingly, the time of day following April 1, 1:59 a.m. is not 2 a.m. but 3 a.m. The period of daylight saving time ends at 2 a.m. on the last Sunday of October, i.e., October 28. Accordingly, the time of day following October 28, 1:59 a.m. is not 2 a.m. but returns to 1 a.m.
The timepiece adapted for daylight saving time automatically advances the standard time by a specified time correction value to indicate daylight saving time during the period of this system. Such a timepiece needs to have set therein information serving to provide a basis for judging whether the current time is within the period of daylight saving time. Generally provided as this information are conditions for a transition from the standard time to daylight saving time (hereinafter referred to as “DST transition conditions”) which are determined for each year and which comprise the starting time and ending time of the period of daylight saving time. In the case of the U.S. in 2001 AD shown in FIG. 7, determined as the DST transition conditions are “the first Sunday of April, 2 a.m.” as the starting time of the period of daylight saving time and “the last Sunday of October, 2 a.m.” as the ending time of the period. The starting time is expressed in the standard time, and the ending time in daylight saving time.
In the case of such a timepiece, the user must seta time of day after turning on the power source. Further in the case where the time indicated differs from the correct time, the user must input the correct time to the timepiece to correct the time setting. Accordingly when the timepiece is to be set or corrected, it is likely that a time that can not exist under the system of daylight saving time will be input. Such a situation is very likely to occur in the case where the timepiece is set immediately after the start of the period of daylight saving time with reference to the indication of a timepiece which is not adapted for daylight saving time or which has not been changed over to this system. After the timepiece has been set, the timepiece counts time based on the time setting. Accordingly, if set erroneously, the timepiece will indicate incorrect times.
For example, reference will be made to the case of the U.S. shown in FIG. 7. When a time during the period of from 2 a.m. to 2:59 of April 1 (Sunday) is input to the timepiece, the input time fulfills the DST transition conditions and is therefore interpreted as being under the system of daylight saving time. However, such a time does not exist under the system of daylight saving time, and the timepiece is set in error.
Timepieces are used not only for indicating times but are used also as incorporated in a main apparatus to supply required time data to the main apparatus. For example, surveillance or monitoring camera devices for capturing images at intervals of a predetermined time period and recording the image data obtained are provided with a timepiece for giving time data to the image data. Such camera devices are intended for surveillance or monitoring for continually recording image data at intervals of a predetermined period of time, the time data for affording information as to the image capturing time must be accurate at all times. Setting the timepiece erroneously must be avoided especially in the case of the timepiece incorporated in the monitoring camera device.
The present invention provides a timepiece which is adapted for daylight saving time so that even if a time erroneous under the system of daylight saving time is set for the timepiece, the input time is automatically corrected for correct time setting, a time setting method for the timepiece, and a monitoring camera device comprising the timepiece.